Method of and apparatus for finishing gear-shaped workpieces



F. HURTH 3,245,320

METHOD OF AND APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES April 12,1966 4 Sheets-Sheet 1 Original Filed July 24, 1962 QmE l/V VENTOR Fri/zHur/h 76(144/ A izalll': ATTORNEY April 12, 1966 F. HURTH 3,245,320

METHOD OF AND APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES OriginalFiled July 24, 1962 4 Sheets-Sheet 3 //VVIVTOR Fri/z Hurfl;

Wau h! #0765,- bllf ATTORNEY F. HURTH 3,245,320

4 Sheets-Sheet 4 his ATTORNEY I M II 51 M M mm 1 T 8 R a m N W In M h E.1 [I Q Q g L Y h In .5- E B E s I .4 .fi QR April 12, 1966 METHOD OFAND APPARATUS FOR FINISHING GEAR-SHAPED WORKPIECES Original Filed July24, 1962 United States Patent 3,245,320 METHOD OF AND APPARATUS FORFINISHING GEAR-SHAPED WORKPIECES Fritz Hurth, Grunwald, near Munich,Germany, assignor to Carl Hnrth, Maschinenund Zahnradfabrik, Munich,Germany Original application July 24, 1962, Ser. No. 212,763. Dividedand this application Dec. 6, 1963, Ser. No. 328,663 Claims priority,application Germany, Aug. 1, 1961,

H 43,302; Sept. 22, 1961, H 43,704 8 Claims. (Cl. 901.6)

This is a division of my application Serial No. 212,763, filed July 24,1962, and now abandoned.

The present invention relates to gear finishing methods in general, andmore particularly to improvements in mounting and positioning of thework holder with respect to the tool holder or vice versa in a gearshaving or another gear finishing machine. Still more particularly, theinvention relates to improvements in a method of crossed-axes shaving ofgear-shaped workpieces.

It is known to provide a gear shaving machine with a spindle whichserves as a means for rapidly advancing one of the holders toward oraway from the other holder and to utilize a cam which advances themovable holder toward the fixed holder when the shaving tool is in orshould be moved into actual engagement with the workpiece. For example,if the work holder is located below and is movable toward and away fromthe tool holder, the cam is rocked step-by-step and is caused to liftthe work holder toward the tool holder in order to move the workpieceinto requisite position with respect to the tool. A serious drawback ofsuch method is that the cam cannot block movements of the work holder ina direction toward the tool holder since the cam actually performs thesole function of lifting the work holder without being in a position tolimit the extent to which the work holder may move toward the toolholder. In other words, such cam merely controls the maximal distancebetween the two holders without being capable of determining the minimaldistance between the tool and the workpiece. Therefore, and if the gearshaving machine or certain of its parts are caused to vibrate or aresubjected to unexpected shocks, the distance between the workpiece andthe tool is likely to be reduced below a permissible minimal distance.Such reduction in distance between the workpiece and the tool cannot becounteracted by a cam which is utilized for moving the work holdertoward the tool holder or vice versa. While the vibrations or shocks arenormally rather small, they can affect the shaving opera tion sinceshaving of gears is a work which must be carried out with a high degreeof precision. For example, vibrations may cause chatter marks in theflanks of teeth on a shaved gear or a similar workpiece.

Accordingly, it is an important object of the present invention toprovide a gear finishing method according to which vibrations, shocksand other undesirable movements of the machine frame and/ or of certainof its toolor work-supporting parts cannot influence the finishingoperation.

Another object of the invention is to provide a gear finishing methodaccording to which the minimal distance between a finishing tool and aworkpiece may be controlled with utmost precision and according to whichsuch minimal distance is maintained under all operating conditions in anextremely simple and reliable manner,

A further object of the invention is to provide a method of determining,maintaining and/ or changing the minimal distance between a work holderand atool holder in all types of gear shaving machines including thosewhich are utilized for crown shaving and/ or for so-called immersionshaving.

ice

In accordance with my method, the teeth of a first gearshaped member areshaved by the teeth of a second gearshaped member in such a way that onemember is caused to move rapidly into meshing engagement with the othermember, that the distance between the axes of the two members isthereupon reduced gradually whereby the teeth of the second memberremove shavings from the teeth of the first member, that the movablemember is gradually moved away from the other member when the removal ofshavings is completed, and that the movable member is thereupon rapidlyreturned to its original position in which the teeth of the first memberare out of mesh with the teeth of the second member. In many instances,gradual return movement of the movable member is preceded by acomparatively short period during which the speed at which the distancebetween the two members is being changed equals or is close to zero sothat the teeth of the second member may treat the teeth of the firstmember without actually removing pronounced shavings therefrom in orderto insure that eventual markings.

or stripes are fully removed from the teeth of the first member beforethe two members are disengaged from each other.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved method itself, however, together with additional features andadvantages thereof, will be best understood from the following detaileddescription of certain specific embodiments with reference to theaccompanying drawings, in which:

FIG. 1 is a side elevational View of a machine for rotary crossed-axesshaving of gears and similar workpieces wherein the blocking means whichcontrols the minimal distance between the work holder and the toolholder comprises a specially configurated rotary plate cam, a portion ofthe machine being broken away to reveal certain parts which drive theblocking cam without any interruptions and which are mounted in theframe and in the work holder;

FIG. 2 is a horizontal section as seen in the direction of arrows fromthe line II-II of FIG. 1;

FIG. 3 is a top .plan view of the machine;

FIG. 3a is a developed view of the blocking cam;

FIG. 3b is a similar developed view of another blocking cam;

FIG. 30 is a developed view of a further blocking cam;

FIG. 4 is a side elevational View of a modified machine which isutilized for crown shaving of gears and similar workpieces, a portion ofthe machine frame and of the work holder being broken away to reveal theconstruction of the drive for the blocking means which is identical withthe blocking means shown in FIGS. 1 to 3;

FIG. 5 is a part front elevational and part vertical sectional view ofthe crown shaving machine, the section of FIG. 5 being taken in thedirection of arrows as seen from the line VV of FIG. 4;

FIG. 6 is a side elevational view of .a further gear shaving machinewherein the blocking means comprises tWo spaced blocking elements whichare fixed to the work holder and which may be moved into abutment withthe tool holder to determine the minimal distance between the axes ofthe workpiece and the tool, a portion of the work holder being shown invertical section;

FIG. 7 is a front elevational view of the machine as seen from theleft-hand side of FIG. 6;

FIG. 8 is a fragmentary section through a tailstock and a cam-shapedblocking element which is adjustably mounted in the tailstock;

FIG. 9 is a larger-scale fragmentary section through the slip clutch ofthe drive for the machine of FIG. 7;

FIG. 10 is a section along the line XX in FIG. 9; and

FIG. 11 an axial section through a worm which is used in the machine ofFIG. 7 and which isbiased by axially operating spring means.

Referring now in greater detail to the illustrated embodiments, andfirst to FIGS. 1 to 3, there is shown a gear shaving machine of theknee-and-column type comprising a frame 10 carrying at the top of itscolumn 10a a horizontal plate 11 which supports a swingable tool holder12, the latter being provided with T-clamps 14 which are slidable in anarcuate T-groove 13 and which enable the tool holder to be fixed to theplate 11 in different positions of adjustment. The holder 12 supports atool 15 which is rotatable about a horizontal axis and which is drivenby an electric motor 16 through-a gear reducer 17 or through a suitabletransmission (not shown).

The front face of the column 10:! is provided with vertical guide meansor ways 18 which make right angles with the plane of the plate 11 andwhich support and guide a work holder including a first slide in theform of a knee 19 in such a way that the slide 19 is reciprocable alongthe ways 18 in directions upwardly toward anddownwardly away from thetool holder 12. The front face of the slide 19 is formed with a verticaldovetailed groove which receives the rail20 of a second slide 21, anditwill be noted that the rail 20 is parallel with the ways 18 to permitthe second slide 21 to move with respect to the first slide 19 indirections toward and away from the tool 15. The gear shaving machine isprovided with means (not shown) for fixing the slide 21 to the slide 19in any of a number of positions of adjustment. The slide 21 carries ahorizontal pivot pin 22 which makes right angles with the longitudinalextension of the ways 18 and which supports a rotary work table 23 fortwo work engaging members here shown as tailstocks 24, 25. Thesetailstocks support a gear-shaped workpiece 26 inthe well known manner.By adjusting the angular position of the table 23, an operator may movethe axis of the workpiece 26 into parallelism with the axis of the tool15, or the axis of the workpiece may cross the axis of the tool,depending upon whether the machine of FIGS. 1 to 3 is utilized forshaving of cylindrical workpieces (such as spur gears) or conicalworkpieces (such as bevel gears). The means for fixing the table 23inany of several positions of inclination with respect to the slide 21 isnot shown in the drawings. It will be noted that the parts 19 to 25together constitute a composite holder for the workpiece 26 and thatthis work holder is located at a level below the tool holder 12 and isoperatively connected with ways 18 in such a manner that it mayreciprocate in a straight path upwardly toward and downwardly away fromthe tool holder.

The frame 10 supports a horizontal cam shaft 28 which is parallel withthe pivot pin 22 and whose forward end carries a blocking means hereshown as a detachable plate cam 27. The shaft 28 is driven by anelectric motor 29 through a multi-stage or infinitely variabletransmission 3!) (as shown in German Patents Nos. 810,565 and 953,930)and through a worm drive including a worm 31 driven by the transmission:and a worm wheel 32 which is mounted on the cam shaft 28. The rear endof the cam shaft 28 carries two control cams 33, 34 which respectivelycooperate with trips of electric switches 36, 35 to regulate theoperation of the shaving machine. For example, the switches 35, 36' maybe respectively connected in the circuits of electric motors 16, 29 toarrest the gear shaving machine after the cam shaft 28 has completed afull revolution.

The blocking cam 27 cooperates with a roller follower 37 which isrotatably mounted on a horizontal bolt 37a carried by the slide 19 andwhich tracks the face of the blocking cam so that the extent to whichthe slide 19' (and hence the workpiece 26) may move upwardly toward thework holder 12 depends on the configuration of the cam 27 which islocated above the follower 37. The latter is biased into permanentcontact with the face of the cam 27 by an advancing means here shown asa resilient package of dished springs 38 which are inserted into anupwardly extending blind bore 1% of the slide- 19 and which rest on thetip of a regulating screw 39. The screw 39 is axially movable in, but isprevented from rotation with respect to the frame 10. The axial positionof the screw 39 may be adjusted by a nut 40 which is rotatably mountedin the frame 10 and which meshes with the screw so that rotation of nut40 will cause axial displacements of the screw 39 toward or away fromthe blocking cam 27, depending upon whether the nut 40 is rotated in aclockwise or anticlockwise direct-ion. It will be readily understoodthat the resilient pack-age 38 may be replaced by a helical spring, by apackage of leaf springs, by a hydraulic system, by a pneumatic system orby other advancing means as long as such advancing means can producerequisite force for moving and for maintaining the follower 37 inengagement with the face of the blocking cam 27. The nut 40 may. beturned by hand or through a suitable motion transmitting mechanism. Forexample, the nut 40 may constitute a worm wheel and is then rotated by aworm with which it forms a drive such as the worm drive 31, 32.

The machine of FIGS. 1 to 3 is utilized for carrying out the method ofmy invention as follows:

In the first step, the operator or operators adjust the position of thetool holder 12 with respect to the plate 11 and the angular position ofthe table 23 with respect to the pivot pin 22. The axis of the tool 15is then either parallel with or crosses the axis of the workpiece 26.The blocking, cam 27 is in its starting position, i.e., it maintains theslide 19 and the tailstocks 24, 25 at such distance from the tool 15that the workpiece 26' may be mounted on the table 23. Once theworkpiece is properly mounted between the tailstocks 24, 25, theoperator starts the motors 16 and'29 whereby the motor 16 drives thetool 15 and the latter may mate with and may rotate the workpiece 26. Inother words, the teeth of the tool 15 are immersed or dip into thespaces between the teeth of the workpiece 26 (hence the name immersionor dipping type of gear shaving). At the same time, the motor 29 drivesthe cam shaft 28 and the latter begins to rotate the blocking cam 27 sothat the cam permits slight upward movement of the slide 19 which issufficient to move the workpiece into requisite position inwhich it isengaged by the tool 15, and the tool removes shavings from the teeth ofthe workpiece. Since the transmission 30 is adjustable, the operator maycause the cam shaft 28 to rotate at different speeds so that theworkpiece 26 may be rather rapidly lifted into operative engagement withthe tool 15, whereupon the angular speed of the blocking cam 27preferably decreases to allow for sufficient time during which the tool15 remains in shaving engagement with the workpiece.

The configuration of the blocking cam 27 is shown in developed view inFIG. 3a. This cam comprises a lobe 27a whose periphery 27b constitutesthe first section of the cam face 27F and which is engaged by the rollerfollower 37 (under the bias of the advancing means 38) when the machineof FIGS. 1 to 3 is at a standstill. The shaft 28 is assumed to drive thecam 27 in a direction as indicated by the arrow 28:: and, when the motor29 is started, the follower 37 begins to track a second section 27c ofthe cam face 27F which extends inwardly toward the axis of the shaft 28(the latter is assumed to be located at a level above the cam 27, asviewed in FIG. 3a) whereby the advancing means 38 compels the workholder 19-25 and hence the workpiece 26 to move upwardly and intomeshing engagement with the tool 15. The inclination of the section 27cis rather pronounced so that the workpiece is moved rapidly into meshingengagement with the tool. The arrangement is preferably such that, whenthe follower 37 has already passed along the first portion 270 andtracks the right-hand portion 270" of the section 270 (as viewed in FIG.3a), the workpiece is advanced into such close proximity of the tool 15that the latters teeth begin to remove shavings from the workpiece. Thesection 27c is followed by a section 27d of very slight inclination,i.e., the section 27d may constitute a portion of a substantiallycylindrical surface which is concentric with the axis of the cam shaft28 so that the distance between the workpiece and the tool remainsunchanged or is reduced very slightly when the follower 37 tracks thesection 27d. During engagement between the section 27d and the follower37, the teeth of the workpiece complete the shaving of the workpiece,and the section 27d is followed by a further section of 272 of slightnegative inclination with respect to the axis of the cam shaft 38. Inother words, while tracking the section 27e, the follower 37 causes theworkpiece 26 to move downwardly and away from the tool 15, thus enablingthe tool to run itself out while the workpiece moves out of compressiveengagement therewith. The last section 27 of the cam face 27F has apronounced negative inclination (i.e., it is inclined in a directionaway from the axis of the cam shaft 28 and leads the follower 37 backonto the first section 27b to thereby disengage the workpiece from thetool and to enable an operator to replace the workpiece by a new one.

The transmission 30 may drive the cam shaft 28 in such a way that, whenthe motor 29 is started, the blocking cam 27 begins to rotate rapidly sothat the follower 37 tracks the first portion 270' of the section 270 ata comparatively high speed, thus enabling the advancing means 38 torapidly lift the workpiece 26 toward the tool 15. The transmission 30shifts into a lower speed when the follower 37 reaches the right-handend of the portion 270' (as viewed in FIG. 3a) so that the movement ofthe workpiece toward the tool 15 is slowed down to a degree necessaryfor maintaining an efficient shaving operation, namely, the workpiece islifted at a speed which is low enough to insure that the serrated teethof the tool 15 are not compelled to remove shavings of excessivethickness. When the follower 37 tracks the section 27d, the speed of thecam shaft 28 may be the same as in the preceding operation during whichthe follower engages the second portion 271: of the section 270. Duringthat stage of the operation when the follower 37 tracks the section 272,the teeth of the tool 15 may remain in mesh with the teeth of theworkpiece 26 so that the latter rotates with the tool while the workholder 19-25 moves slowly downwardly and away from the tool holder 12.Such engagement between the teeth of the workpiece and the tool whilethe follower tracks the section 27e is advisable because the teeth ofthe tool are then in a position to remove markings or scratches from theteeth of the workpiece. Such markings can develop during that stage ofoperation when the tool removes shavings because the work holder isbeing caused to move toward the work holder to reduce the distancebetween the axes of the tool and the workpiece.

In the last stage of the operation, the transmission 30 again shiftsinto high speed and the follower 37 is caused to travel rapidly alongthe section 27 in order to return into engagement with the lobe 27a ofthe blocking cam (section 27b) whereby the blocking cam causes theworkpiece to descend rapidly away from and out of mesh with the tool 15,and the cam arrests the work holder at such disctance from the toolholder which is sufiicient to permit convenient removal of the workpiecefrom the tailstocks 24, 25.

It will be noted that, when the blocking cam 27 completes a fullrevolution, the tool 15 has completed the shaving of a workpiece and thecontrol cams 33, 34 may arrest the motors 16, 29 while the operatorreplaces the finished workpiece by a new one.

In accordance with a slight modification which is so obvious that it canbe readily comprehended without a separate illustration, theconfiguration of the blocking cam 27 may be simplified in the followingmanner:

The face of this cam may consist of three sections,

namely, a first section 27b which surrounds the cam lobe 27a, a secondsection 270 of positive inclination with respect to the axis of the camshaft 28, and a third section 27) of negative inclination. Thus, thesection 27d of FIG. 3a may form part of the section 27c, and the section27e may form part of the section 27 In such instance, the last portionof the section 27c may perform the function of the section 27a incooperation with the transmission 30 which drives the cam shaft 28 at aspeed which is sufficiently slow to insure that the teeth of the toolmay properly remove shavings from the teeth of the workpiece. In thezone of transistion between the last portion of the section 27c and thefirst portion (corresponding to the setcion 27e of FIG. 3a) of thesection 27 the work hold-er 19-25 then reverses the direction of itsmovement while the transmission 30 continues to drive the cam shaft 28at a slow speed so that initial disengagement between the workpiece andthe tool is gradual which enables the teeth of the tool to removeeventual markings from the teeth of the workpiece. The last portion ofthe section 27 on such a modified blocking cam is tracked while the camshaft 28 is driven at a higher speed so that the workpiece is movedrapidly out of actual mesh with the tool and assumes a position in whichit can be removed from the tailstocks 24, 25. In other Words, suchmodified blocking cam is utilized in combination with a transmissionwhich regulates the speed of the cam shaft 28 in a sense to insure thatthe shaving operation is carried out in the same way as described inconnection with FIG. 3a. Thus, while the configuration of the face onthe blocking cam is simplified, the various speed at which thetransmission 30 drives the cam shaft 28 must be regulated by a morecomplicated mechanism.

The rotary blocking cam 27 may be replaced by a socalled wedge cam whichmoves back and forth and which controls the minimal distance between theworkpiece and the tool while performing a linear rather than a rotarymovement. If the blocking means is a wedge-like cam, the operativeconnection between the motor 29 and the block ing means is changed insuch a way that the blocking means moves continuously in a linear pathand that its cam face may control the position of the slide 19 withrespect to the ways 18 in a manner analogous to that described above.

It will be noted that the blocking cam 27 cooperates with the follower37 of the work holder 19-25 to determine the minimal distance betweenthe work holder and the tool holder 12 against the action of theadvancing means 38 so that vibration of the frame 10 or of one or bothholders can have no bearings on the minimal axial distance between thetool and the workpiece, particularly during such intervals when theworkpiece is actually shaved by the teeth of the tool 15. The principleis the same if the position of the workpiece and of the tool 15 isreversed, i.e., if the workpiece is mounted in the holder 12 and if thetool is mounted in the holder 19-25. The heretofore described feature ofthe machine resides in the provision of means which blocks areciprocable holder against excessive movements in a direction towardthe fixed holder, regardless of whether the tool is mounted in thereciprocable holder or in the fixed holder.

FIG. 3!) illustrates a somewhat different blocking cam 127 whose camface 127A is very similar to the cam face 27F of the cam 27, exceptingthat the section 27c isreplaced by two mutually inclined sections 1270',127C". The remaining sections 27b, 270., 27c and 27 of the cam face 127Fare identical with the corresponding sections of the cam face 27F. Thesection 1270 is tracked by the follower 37 when the transmission 30drives the cam shaft 28 at a fixed speed in order to permit rapidadvance of the work holder 1925 toward the tool holder 12. When thefollower 37 tracks the section 127c", the teeth of the tool 15 removeshavings from the teeth of theworkpiece, and such removal of shavingscontinues while the follower tracks the section 27d. When the followertracks the section 272, the teeth of the tool remove markings from theteeth of the workpiece, and the follower 37 rolls along the last section27 when the workpiece is caused to rapidly return to its originalposition in which it may be removed from the tailstocks. An importantadvantage of the earn 127 is that the transmission 30 may drive theshaft 29 at constant speed, i.e., the machine may utilize a greatlysimplified transmission because the configuration of the cam 127F byitself insures that the speed at which the workpiece moves toward andaway from the tool is regulated in a manner as described in connectionwith FIG. 3a and that the duration of engagement between the teeth ofthe workpiece and of the shaving tool is sufiicient to insuresatisfactory removal of shavings and eradication of any markings whichmight have remained after the tool has ceased to remove shavings(section 27c).

FIG. 30 illustrates a blocking cam 227 whose face 227F changes its:inclination gradually, i.e., without such pronounced transitions asshown between certain sections of the cam face 27F or 127F. The sections227b, 2271;, 2270", 227d, 2272 and 227) of the cam face 227Frespectively correspond to the sections 27b, 127c, 1270", 27d, 272 and27 of the cam face 127R It should be mentioned here that the cam 27, 127 or 227 is equally useful in convenient gear finishing machines of thetype described in the introductory part of this disclosure, namely, inwhich the cam serves as a means for determining the maximal distancebetween the work holder and the tool holder and wherein the camcooperates with a follower which is biased by a spring or by anotheradvancing means in a sense to move the work holder away from the toolholder. This will be readily understood since, and insofar as theregulation of the shaving operation is concerned (to wit: bydisregarding the feature that the cam may serve as a blocking meanswhich determines the minimal distance between the workpiece and thetool), the cam 27, 127 or 227 will regulate movements of the workpieceinto engagement with or away from the tool (or vice versa) if the camserves as an advancing rather than as a blocking means. For example, allthat is necessary is to mount the cam 27 of FIG. 1 at a level below theslide Hand to mount the resilient package 38 in the slide 19 in such away that it biases the follower downwardly and into engagement with theface of the cam. In fact, if the cam is mounted in such a way that itcontrols the maximal distance between the work holder and the toolholder, the package 38 may be omitted altogether and the follower 37 ofthe work holder 19-25 may rest by gravity on the cam face 27F.

Before proceeding with the description of certain other features of myinvention, I will point out the advantages of the method which wasdescribed in connection with FIGS. 3a to 30. Heretofore, it wascustomary to control movements of the tool into shaving engagement witha workpiece or vice versa by means of a variable speed motor, i.e., itwas necessary to shift into different speeds if the operator desired toalter the speed at which the axes of the workpiece and of the tool weremoved toward each other. Such operation is time-consuming and the teethof the tool invariably leave some markings on the teeth of the tool,particularly if the shaving operation is carried out by the immersionprocess. Attempts were made to improve the operation of such shavingmachines by special distribution of shaving edges on the teeth of thetool in a manner as disclosed in copending application Serial No.158,407 of Fritz Hurth and assigned to the same assignee. While suchdistribution of shaving edges brings about substantial improvements inthe shaving operation, the machine is more complicated because the rateat which the workpiece is moved in stepwise fashion toward the tool orvice versa depends on the distribution of cutting edges on the teeth ofthe shaving tool.

By providing a movable cam whose rotary or reciprocatory movement is notinterrupted while it causes the workpiece to move toward the shavingtool or vice versa,

I provide a very simple and highly satisfactory method of preventing theformation of markings on the teeth of the workpiece. This, and asdescribed in connection with FIGS. 1 to 3, movements of the cam 27, 127or 227 need not be interrupted at all at the time the cam causes one ofthe holders to reduce the distance between the axes of the tool and theworkpiece. In other words, the cam moves uninterruptedly all the timewhile the workpiece is being moved toward and while the teeth of theworkpiece remain in engagement with and are being treated by the teethof the tool. In fact, and as explained hereinabove, movements of the camneed not be interrupted at all from the very start and all the way tothe end of a shaving operation including movements of the workpiece intoand out of mesh with the shaving tool. Therefore, the likelihood thatthe shaving tool would leave undesirable scratches or other markings onthe teeth of the workpiece is very remote, and it was found that themethod of my invention actually insures that the tool can treat theteeth of the workpiece to exceptionally high degree of precision finish.

The important feature of my method resides in that the distance betweenthe axes of the workpiece and the tool is being reduced continuously upto the very moment when the shaving operation is completed so that it isnot necessary to interrupt the advance of the tool toward the workpieceor vice versa. The speed at which the two gearshaped members move towardeach other may be varied by interposing a transmission in the power linebetween a constantly driven motor and the cam and/ or by imparting tothe cam face a configuration which insures that the speed at which thedistance between the two gear-shaped members is being reduced is changedwhenever necessary to insure that the teeth of the workpiece are shavedto an exceptionally high degree of precision finish.

The reason for reducing the speed at which the two gear-shaped membersare being moved toward each other at the time when the shaving operationis about to be or is actually completed is that, otherwise, it would benecessary to immediately reverse the direction of movement when theremoval of shavings is completed. Such rapid reversal in the directionof movement of the workpiece with respect to the tool or vice versawould invariably produce some markings on the teeth of the workpieceand, therefore, by utilizing a cam whose face or whose drive meansinsures that the transition between forward speed and return speed ofthe movable holder is gradual I provide a method according to which theperiods of idleness between consecutive stages of a shaving operationare reduced to zero and wherein the workpieces may be treated to ahigher degree of precision finish than in all such gear shaving machinesof which I am aware at this time.

In the embodiment of FIG. 3a, gradual transition between forward andreturn movements of the movable work holder-1925 takes place when thefollower 37 tracks the sections 27a, 27a of the cam face 27F, wherebythe speed at which the distance between the axes of the tool 15 andworkpiece 26 changes while the follower tracks the sections 27d, 27e isclose to zero. This obviously insures that the transition betweenforward and return movements of the work holder 19-25 is gradual and thetool cannot cause undesirable scratches on the teeth of the workpiece.

I have found that, when a shaving operation is being carried out, it isundesirable to maintain the distance between the workpiece and the toolunchanged for an extensive period of time because the tool then producesso-called zebra stripes in the teeth of the workpiece. In order to avoidthe formation of such stripes, my method is preferably carried out insuch a way that the interval of time during which the forward or returnspeed of the movable holder equals zero is very short, that such shortinterval of zero speed is preceded by an interval (cam section 270. inFIG. 3a) during which the forward speed of the movable holder is low,and that such short interval of zero speed is followed by an interval(cam section 27e in FIG. 3a) during which the return movement of theholder takes place at low speed. Regardless of whether the gear shavingmachine utilizes a rotary plate cam of the type shown in FIGS. 3a to 30or a movable wedge cam, its cam face is configurated in such a way thatthe transition between high forward speed (cam face section 27c) andhigh return speed (cam face section 277") is always smooth so that zerospeed is reached and passed gradually (cam face sections 27d, 27c).

Of course, and as explained hereinabove, the same effect can be obtainedeven if the transition between the positive and negative inclinations ofthe cam face is abrupt, as long as the speed at which the cam is movedis regulated in such a way that the forward speed of the movable holderis reduced gradually before it drops to zero speed and that returnmovement of the movable holder immediately following zero speed is alsogradual. This can be achieved by utilizing a transmission which canchange the speed of cam movement to compensate for omission of certaincam face sections such as the sections 27d, 272 of the cam face 27fshown in FIG. 3a. However, if the cam face is configurated in a manneras shown in FIGS. 3a to 30, the cam is capable of regu lating theforward and return speeds of the movable holder without necessarilychanging the speed of its angular or linear movement.

FIGS. 4 and 5 illustrate a modified gear having machine whose frame 110comprises a column 110a and a head 11011, the latter mounting anadjustable holder 55 for the tool 115. In contrast to the constructionof the machine shown in FIGS. 1 to 3, the modified machine is assembledin such a way that the workpiece 126 is reciprocable in its holder indirections parallel with the axis of the tool 115 and, in addition, thework holder is reciprocable in a straight path in directions toward andaway from the tool holder 55. The manner in which the slide 1 isreciprocable along vertical ways provided on the front face of thecolumn 110a is the same as described in connection with FIGS. 1 to 3,and the front face of the slide 19 is again provided with a verticalgroove for the rail 20 of a second slide 21 which carries a fixedhousing 40 for the vertical shaft of a rotary carriage 41 supporting areciprocable slide 42 which carries a pivotable base plate 43 for atiltable table 44. Rocking movements of the table 44 are controlled by arocking device including an adjustable guide bar 45 which is receivedbetween three rollers 46 supported on the table 44 in a manner asdescribed in copending application Serial No. 130,624, of Otto Rogg,assigned to the same assignee. The bar 45 may be fixed to the housing 40in a number of different angular positions and rocks the table 44 insynchronism with longitudinal displacements of the slide 42.

The table 44 is reciprocated by an electric motor 47 mounted on thehousing 40 and by a gear train including two mating spur gears 48 whichact as a gear reducer and one of which is directly driven by the outputshaft of the motor 47, a pair of mating spur gears 49 which act as areversing gear, two pairs of mating bevel gears 50, 51, a third pair ofmating spur gears 52 one of which drives a horizontal spindle 53, thelatter mounted in the carriage 41 and meshing with a spindle nut 54which is fixed to and which extends downwardly from the slide 42. Theadjustable holder 55 enables the tool 115 to assume a position in whichits axis crosses the axis of the workpiece 126, the latter mounted intailstocks 24, carried by the tiltable table 44. The machine of FIGS. 4and 5 is utilized for crown shaving. If desired, the tailstocks 24, 25may be mounted on a plate which is then tiltably supported by the table44. The operation of such crown shaving machines is known and need notbe described in greater detail. The tool 115 is driven by a suitablemotor, for example, in a manner as illustrated in FIGS. 1 to 3, androtates the workpiece 126 when the latter is lifted by the slide 19 intothe range of teeth on the tool. At the same time, the motor 47 drivesthe gear train 48-54 and brings about reciprocatory movements of theworkpiece 126 with respect to the tool.

The blocking means 27 and the advancing means 38 in the gear shavingmachine of FIGS. 4 and 5 are identical with the corresponding blockingand advancing means of FIGS. 1 to 3a excepting that one of the switches35, 36 may control the motor 47. The blocking cam 27 again cooperateswith the roller follower 37 and operates against the action of theadvancing means 38 to limit movements of the workpiece 126 in adirection toward the tool 115. Any movements of the workpiece in adirection away from the tool are possible only by overcoming the bias ofthe advancing means 38. The composite tool holder of the machine shownin FIGS. 4 and 5 includes the parts 19-21, 24, 25 and 4044. The meansfor driving the blocking cam 27 is the same as in the machine of FIGS. 1to 3, and the face of the blocking cam may assume a configuration asshown in FIG. 3a, 311 or 30.

In the gear shaving machine of FIGS. 4 and 5 in which the workpiece isreciprocated with respect to a rotating gear-shaped tool, the formationof zebra stripes is fully avoided if the face of the blocking cam 27assumes a configuration as shown in FIGS. 3a to 30. Such cam insuresthat the teeth of the workpiece and of the tool are slightly separatedbefore the workpiece is rapidly returned to its original position ofdisengagement from the tool 115. Heretofore, such crown shaving machineswere operated in such a way that the workpiece was caused to reciprocatewith respect to the revolving tool after the latter has completed theactual shaving operation in order to make sure that the tool wouldremove all stripes from the teeth of the workpiece. Such additionalreciprocation 0f the workpiece consumes much time and reduces the outputof the crown shaving machine. In accordance with my invention, removalof eventual stripes from the teeth of a shaved workpiece takes place atthe time when the workpiece is moved gradually away from the tool orvice versa.

FIGS. 6 and 7 illustrate a different gear shaving machine whichcomprises a frame 61 having a head 61b for an adjustable tool holder 62.The machine of FIGS. 6 and 7 is of the vertical knee-and-column type,and the holder 62 enables the tool 215 to assume a number of differentpositions with respect to the workpiece 226. The means for driving thetool 215 is known in this art and, therefore, is not illustrated in thedrawings.

The column 61a of the frame 61 supports a vertically reciprocable slide63 which is movable along vertical ways 64. The slide 63 supports a worktable 65 which is tiltable about a horizontal pivot pin 66, the lattermaking right angles with the longitudinal extensions of the ways 64. Thetable 65 carries two tailstocks 67, 68 for the workpiece 226, and thearrangement is preferably such that the axis of the workpiece 226crosses the axis of and is driven by the tool 215 when the machine is inoperation. The extent to which the table 65 may be rocked about thepivot pin 66 is regulatable by two screws 69, 70 which are mounted onthe slide 63 and whose tips are located beneath the table 65 at theopposite sides of the pivot pin 66. As a rule, the play of the table 65with respect to the screws 69, 70 is rather small.

The tailstocks 67, 68 respectively support substantially prismaticblocking elements 71, 71a, and portions of these blocking elementsextend into upwardly opening cutouts or recesses provided in therespective tailstocks to be retained in requisite position by clampingscrews 72. The elements 71, 71a are preferably located at the oppositesides of and in close or immediate proximity of the tool 215 to insurethat the relative position of the axis of the workpiece 226 with respectto the tool axis remains unchanged irrespective of elastic deformationof the work and tool holders. The slide 63 is reciprocable along itsways 64 by a vertical spindle 73 which'is mounted on the base 610 of theframe 61 and which may be driven by an electric motor 74- or by ahandwheel 75 through a suitable transmission accomodated in the interiorof the slide 63. Since the motor 74 or the handwheel 75 must advance theblocking elements 71, 71a into abutment with a fixed part, i.e., withthe tool holder 62 or with another component which is rigid with theframe 61,,the transmission mounted in the slide 63 preferably comprisesa suitable slip clutch 74a, i.e., a friction clutch or the like whichpermits the motor 74 or the handwheel 75 to rotate with respect to thespindle 73 when the blocking elements 71, 71a prevent further ascent ofthe work holder. Combined with that part of the slip clutch which slideswith respect to the motor is a gear member 85 which drives a worm gear88 through a gear 86 which is preferably shiftable, and through a worm87. The worm gear 88 is a spindle nut in mesh with the spindle 73. FIG.9 shows on a larger scale a section through the slip clutch'andillustrates that the slidablegear member 85 is'provided with one or morecam means 89. A switch 91 provided on a member 90 of the clutch isconnected with the motor. The switch sends an impulse as soon' asone ofthe cam means 89 operates a control member 92 mounted in the member 90.Thus, the switch 91 will at once switch off the drive (motor 74) for theslide 63 or will switch on a time-lag relay which will switch off themotor 74 after a predetermined period of time and eventually initiatereturn movement as soon as the relative movement between motor 74 andthe gear member 89 is terminated. In order to avoid the provision of aslip clutch for damping the impact the worm 87 may be axially shiftableand may be elastically supported (FIG. 11) in a manner as disclosed inGerman Patent 1,108,543 or in US. Patent 2,945,925. If desired, bothmethods may be combined. The worm 87 can operate a switch 87a.

The machine of FIGS. 6 and 7 need not comprise means for reciprocatingthe workpiece 226 with respect to the tool 215 because it is assumedthat the axial length of the tool is sufficient to engage the workpiecealong the full length thereof (see FIG. 7). In addition, the tool 215 isassumed to be a hyperboloidal gear so that the shaving operation may becarried out on the so-called dipping or immersion principle.

The distance between the axes of finished workpiece 226 and tool 215 isdetermined by the dimensions of exchangeable blocking elements 71, 71a.If the distance between the surfaces 76, 77 on the tailstocks 67, 68(which abut against the undersides of the elements 71, 71a) and thecorresponding surfaces 78, 79 (which abut against the upper sides of theelements 71, 71a) is the same, both blocking elements are of identicalheight provided, of course, that the workpiece 226 is a cylindrical spurgear. If the workpiece is a bevel gear, the height of one block ingelement exceeds the height of the other blocking e1ement so that theaxis of the workpiece may be properly inclined with respect to the axisof the tool 215. Each blocking element may consist of several sectionswhich may be separated from each other when it becomes necessary toreduce the minimal distance between the tool and the workpiece.

The machine of FIGS. 6 and 7 is used for carrying out my improved methodas follows:

It is assumed that the workpiece 226 is a cylindrical spur gear. In thefirst step, the slide 63 is moved downwardly (either by starting themotor 74 or by manually operating the wheel 75) in order to permitinsertion of the workpiece 226 between the tailstocks 67, 68. The screws69, 70 are adjusted in such a way that there remains some play betweentheir tips and the table 65 which is sufiicient to permit properadjustments in the position of the table depending on the type ofblocking elements 71, 71a momentarily used in the machine. In

the next step, the elements 71, 71a are clamped in the recesses of therespective tailstocks so that they may determine the shortest distancebetween the axes of the workpiece 226 and tool 215 as soon as theirupper sides engage the surfaces 78, 79. Once the workpiece 226 and theblocking elements 71, 71a are properly mounted in the tailstocks 67, 68the drive for the tool 215 is started to rotate the tool, and the motor74 is also started to move the slide 63 in upward direction and tothereby advance the workpiece into mesh with the tool. Upward movementof the workpiece is terminated when the blocking elements 71, 71a abutagainst the surfaces 78, 79 and the height of these blocking elements isselected in such a way that the teeth of the tool 215 remove shavingsfrom the teeth of the workpiece when the blocking elements engage theholder 62. The maximal distance be tween the holder 62 and the slide 63need not exceed the minimal distance at which the workpiece may beconveniently removed from the tailstocks 67, 68.

Of course, at the time the blocking elements 71, 71a move'into actualabutment with the tool holder 62', there develop some compressivestresses between the tool and the workpiece, but such stresses diminishat the same rate at which the tool removes shaving from the workpiece sothat all stresses are eliminated upon completion of theshaving-operation. The slip clutch in the aforementioned transmissionbetween the motor 74 and spindle 73" enables the motor or the handwheelto biasthe blocking elements 71, 71a into constant abutment with thetool holder 62.. Such bias of the parts 73, 74, 74a eliminates any playbetween the tool holder 62 and the work holder 63-68. It will be notedthat the parts 73, 74, 74a constitute an advancing means for the workholder 63-68 whose function is equivalent to the function of advancingmeans 38.

The machine of FIGS. 6 and 7 may be readily modified in a number of wayswithout departing from the scope of my invention. For example, theworkpiece 226-may reciprocate with respect to the tool 215 in a manneranalogous to that described in connection with FIGS. 4 and 5. In suchinstances, prismatic blocking elements 71, 71a are preferably replacedby rollers to reduce friction with the tool holder when the workpieceand its holder are caused to reciprocate with respect to the toolholder. Furthermore, the blocking elements 71, 71:! may assume the formof eccentric cams which are adjustably mounted in the tailstocks or inanother part of the work holder so that, merely by angularly displacingthe cams, an operator may convert the machine for shaving of differentlyconfigurated or dimensioned workpieces. If necessary, such cams may beadjusted in the course of a shaving operation in order to change theminimal distance between the workpiece and the tool in accordance with apredetermined work schedule which may be analogous with the workschedule controlled, for example, by the blocking cam 27 of FIG. 321.FIG. 8 shows a tailstock 167 which is provided with a recess 167a for aneccentrically mounted blocking element in the form of a plate cam 171.This cam is supported on a rotary eccentric shaft 171A. The position ofthe eccentric shaft can be regulated by means of a worm gear 172 and aworm 172a. The latter can be driven either manually or by a motor (notshown). The motor can be automatically controlled according to a programwhich corresponds to that described in connection with FIGS. 3a, 3b, 30.To arrest the eccentric shaft, a clamp 1721) may be provided. Inaddition to this, a graduated scale as well as a pointer 1720 may beprovided to enable the operator to tread the turning angle. The pointermay be mounted on the worm gear or on the worm. The camisrotatable withthe shaft 171A and may be arrested in any of an infinite number ofpositions by the clamp 17211 which is mounted in the tailstock 167. Thetailstock may be provided with a graduated scale and the cam 171' may beprovided with a pointer to facilitate its adjustment if the machine isconverted for treatment of different workpieces. The other tailstock(not shown in FIG'. 8) is combined with a second blocking cam which isidentical with the cam 171.

The blocking cam or cams may be combined with the spindle 73, or theupper end of this spindle may assume the shape of a cam to insuregradual transition between forward and return movements of theworkpiece.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic and specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be seuured by Letters Patent is:

1. A method of shaving the teeth of a first gear-shaped member byengagement with the teeth of a second gearshaped member, comprising afirst step of rotating one of said members; a second step ofcontinuously and gradually reducing the distance between said members tointermesh the teeth thereof whereby said one member rotates the othermember and the teeth of said second member remove shavings from theteeth of said first member; and a third step of continuously andgradually increasing the distance between said members with a gradualtransition from said second step to said third step.

2. A method of shaving the teeth of a first gearshaped member byengagement with the teeth of a second gear-shaped member, comprising thesteps of supporting said members in such a way that the axis of saidfirst member crosses the axis of said second member; rotating one ofsaid members about the axis thereof; and continuously and graduallyreducing the distance between the axes of said members first at a higherspeed to rapidly intermesh the teeth thereof whereby said one memberdrives the other member and thereupon at a reduced speed whereby theteeth of said second member remove shavings from the teeth of said firstmember.

3. A method of shaving the teeth of a first gear-shaped member byengagement with the teeth of a second gearshaped member, comprising thesteps of supporting said members in such a way that the axis of saidfirst member crosses the axis of said second member; rotating one ofsaid members about the axis thereof; continuously reducing the distancebetween the axes of said members to intermesh the teeth thereof wherebythe teeth of said second member remove shavings from the teeth of saidfirst member; thereupon maintaining the distance between the axes ofsaid members at a substantially constant magnitude while the teeth ofsaid second member remain in mesh with and remove from the teeth of saidfirst member any markings which might have developed during shaving ofsaid first member; and thereupon continuously increasing the distancebetween the axes of said members, first at a lesser speed and thereuponat a higher speed, until the teeth of said members are out of mesh witheach other.

4. A method of shaving the teeth of a first gear-shaped member byengagement with [1 6 th of a second gearshaped member, comprising thesteps of supporting said members in such a way that the axis of saidfirst member crosses the axis of said second member; rotating one ofsaid members about the axis thereof; and continuously reducing thedistance between the axes of said members first at a higher speed tointermesh the teeth thereof whereby the teeth of said second memberremove shavings from the teeth of said first member, and thereupon at areduced speed so that the teeth of said second member continue to removeshavings from the teeth of said first memher.

5. A method of shaving the teeth of a first gear-shaped member byengagement with the teeth of a second gearshaped member, comprising thesteps of supporting said members in such a way that the axis of saidfirst member crosses the axis of said second member; rotating one ofsaid members about the axis thereof; continuously reducing the distancebetween the axes of said members first at a higher speed to intermeshthe teeth thereof and thereupon at a reduced speed whereby said onemember rotates the other member and the teeth of said second memberremove shavings from the teeth of said first member; thereuponmaintaining the distance between the axes of said members at asubstantially constant value whereby the teeth of said second membercontinue to mesh with and to treat the teeth of said first member; andcontinuously increasing the distance between the axes of said membersfirst at a lesser speed and thereupon at a higher speed until the teethof said members are out of mesh with each other.

6. A method of shaving the teeth of a first gear-shaped member byengagement with the teeth of a second gearshaped member, comprising thesteps of supporting said members in such a way that the axis of saidfirst member crosses the axis of said second member; rotating one ofsaid members about the axis thereof; continuously reducing the distancebetween the axes of said members first at a higher speed to intermeshthe teeth thereof whereby the teeth of said second member removeshavings from the teeth of said first member and thereupon at a greatlyreduced speed while the teeth of said second member continue to meshwith and to treat the teeth of said first member; thereupon continuouslyincreasing the distance between the axes of said members first at alesser speed and thereupon at a higher speed until the teeth of saidmembers are disengaged from each other.

7. A method of crown shaving as set forth in claim 6, further comprisingthe step of reciprocating one of said members in the axis directionthereof.

8. A method as set forth in claim 7, further comprising the step ofrocking said one member about an axis making right angles with thedirection of reciprocatory movement of said one member.

References Cited by the Examiner UNITED STATES PATENTS 2,387,679 10/1945Praeg -l.6 3,115,064 12/1963 Rogg 90-1.6 3,118,343 1/1964 Ketzler 901.63,143,039 8/1964 Mills 901.6

WILLIAM W. DYER, JR., Primary Examiner.

GERALD A. DOST, Assistant Examiner,

1. A METHOD OF SHAVING THE TEETH OF A FIRST GEAR-SHAPED MEMBER BYENGAGEMENT WITH THE TEETH OF A SECOND GEARSHAPED MEMBER, COMPRISING AFIRST STEP OF ROTATING ONE OF SAID MEMBERS; A SECOND STEP OFCONTINUOUSLY AND GRADUALLY REDUCING THE DISTANCE BETWEEN SAID MEMBERS TOINTERMESH THE TEETH THEREOF WHEREBY SAID ONE MEMBER ROTATES THE OTHERMEMBER AND THE TEETH OF SAID SECOND MEMBER REMOVE SHAVINGS FROM THETEETH OF SAID FIRST MEMBER; AND A THIRD STEP OF CONTINUOUSLY ANDGRADUALLY INCREASING THE DISTANCE BETWEEN SAID MEMBERS WITH A GRADUALTRANSITION FROM SAID SECOND STEP TO SAID THIRD STEP.